Nerve and muscle weakness. Be diagnosed?

2 years ago I lost the urge and necessary force required for bowel movement, urine urge also not there but urine happens usually when I go to bath room. I have neck and lower back  stiffness and pain. Done MRI of lower back twice and neck thrice. 7 months ago , I got an MRI done for brain and spine which was normal with mild cervical disc bulge and loss of lordosis. Doctor said nerve and muscle weakness are functional. But the weakness has progressively increased. Extreme loss of strength in hands and legs, palm and feet some times feel loss of sensation and extremely light. There is dryness also which feels in legs, palms, feet and forehead and cheeks. Hand and legs are thinning. Doctors are giving medicines like neuro multivitamin, pregabilin or symbol 20 but my stomach can't tolerate it for more than 2-3 days. What could be the disease which can't be diagnosed?